Surface interactions between embryonic cells are believed to play an important role in human development. Lactosaminoglycans have been identified as a major developmentally-regulated cell surface component of early mammalian embryos, and simple sugar addition modifications of terminal sequences are known to generate many stage-specific differentiation antigens. The proposed research will test two hypotheses regarding the functional role of lactosaminoglycans in embryogenesis: (1) that they provide multivalent ligands for embryonic cell interactions, and (2) that they constitute an embryonic cell surface "marking system", reflecting specific cell lineage commitments or differentiated membrane functions. Hypothesis 1. (a) Purified X haptens (GalBeta1-4[FucAlpha1-3]GlcNAcBeta1-R) will be used as competitive inhibitors to test whether the Alpha1-3 fucosylation of lactosaminoglycan is required for the correct alignment of blastomeres during compaction. (b) The membrane glycoproteins in embryonal carcinoma (EC) cells that carry lactosaminoglycan will be purified by immunoaffinity chromatography. These lactosaminoglycan conjugates will then be used as probes to identify lactosaminoglycan binding molecules in the membranes of EC cells by affinity chromatography and ligand blot labeling. Hypothesis 2. (a) Subpopulations of pluripotent EC cells expressing predominantly mono-, di-, or tri-fucosylated lactosaminoglycan chains will be selected using well-characterized monoclonal antibodies by fluorescence-activated cell sorting and by cloning. The differentiation potential of these subpopulations will be examined both in vitro and in vivo. (b) The origin of migrating mesoderm cells in the early postimplantation mouse embryo will be determined using monoclonal antibody C6 and immunohistochemical techniques. (c) Anti-band III antibody will be reacted with Western blots of affinity-purified lactosaminoglycan conjugates to test whether the lactosaminoglycan or murine EC cells, like the lactosaminoglycan of human erythrocytes, is carried predominantly on a band III-homologous protein (the transmembrane ion-exchange protein). In summary, these studies are directed at understanding the fundamental mechanisms of morphogenesis and differentiation. The results may eventually contribute to the prevention of congenital malformations and malignancy.